This invention relates to an electric motor and a method and an apparatus for manufacturing the electric motor and, more particularly, to the structure of a connection between an enamel-coated wire (hereinafter referred to as "enameled wire") forming a winding of an electric motor and a lead and a method and an apparatus for forming the connection.
An electric motor has at least one winding which is ordinarily formed of an enameled wire. The electric motor also has leads for connecting the ends of the winding to a power source. According to the prior art, when leads are connected to the winding, a preparatory operation of removing an enamel coating from end portions of the enameled wire to which the leads are to be connected is performed based on a method such as that as shown in FIG. 5 or 6. In the conventional enamel removing method shown in FIG. 5, an end portion 31a of an enamel coating 31 of an enameled wire 30 is forcibly stripped off a conductor 32 by stripping with knife edges 35 while the enameled wire 30 is retained by a fixing member 34. In the conventional enamel removing method shown in FIG. 6, metallic brushes 36 or grinding stones (not shown) are rotated to scrape enamel off a conductor 32 of an enameled wire 30 at an end portion 31a. Means for removing, enamel other than those shown in FIGS. 5 and 6, for example, means for burning enamel b flame to remove the enamel and means for removing enamel by a chemical remover are known.
In the prior art, enameled wire 30 with enamel coating stripped from its end portions by such means is wound around a lead 7, as shown in FIGS. 7 and 8. Then, end portions of conductors 32 and 6 of the wires 30 and 7 are welded together as at 8 in the method shown in FIG. 7, or the conductors 32 and 6 are connected by a brazing material 9 in the method shown in FIG. 8. The conventional method shown in FIG. 7, however, has a problem that the conductor 32 is melted by the welding heat at a portion 15 of the conductor 32 adjacent to the welded portion 8 so that this portion is reduced in diameter or the mechanical strength of the wire is reduced by thermal stress, and there is therefore a risk of an occurrence of disconnection during operation of the electric motor. The conventional method shown in FIG. 8 also has a problem of melting and a reduction in the thickness of a portion 16 of the conductor 32 adjacent to the brazing material 9 caused by heating during brazing, with a resultant risk of disconnection.
Each of the above-mentioned conventional enamel removing means badly influences the conductor so as to reduce the connection strength of portions connected by brazing or soldering, resulting in a reduction in the reliability of the connection. Further, it is difficult to accurately control the length of the enamel coating to be stripped. Because of these problems, automatization of connecting operations is difficult. That is, in the case of the enamel removing means shown in FIG. 5, there are large possibilities that the conductor 32 of the portion stripped of enamel is scraped together with enamel 31 so that its cross-section is reduced and that the stripping knife edges 35 bite into the conductor 32 and draw the same since the knife edges scrape off the enamel 30 while the enameled wire 31 is retained by the fixing portion 34. In the case of the..enamel removing means shown in FIG. 6, it is likely that the conductor 32 is ground and damaged or reduced in thickness when the enamel 31 is scraped off, and that a force in a rotational direction is applied to the enameled wire 30 so that enameled wire 30 is wrung. In the case of the means for removing enamel by burning in flame, the conductor is oxidized by flame, so that the connection strength is reduced and the connection reliability is considerably reduced if leads are connected by brazing or soldering. In addition, enamel is removed excessively out of the desired enamel removing range. In the case of the means for removing enamel by melting the enamel by a chemical remover, the surface of the conductor is corroded, so that the strength of the brazed or soldered connection is reduced. In addition, it is difficult to accurately adjust the length of the enamel to be removed.